Packaging of semiconductor chips

ABSTRACT

A semiconductor device is fabricated by placing a semiconductor chip in a lead frame which has no die pad. Electrodes of the chip are connected by bonding wires to respective lead fingers. Additionally, the lead frame has movement restricting fingers which limit horizontal movement of the chip within the lead frame during injection of resin into a mold surrounding the chip. Furthermore, the mold has horizontal movement restricting projections to limit vertical movement of the chip within the mold cavity. The restriction on horizontal and vertical movement of the chip reduces the risk of the bonding wires being broken or short circuited during the resin injection process.

This is a division, of application Ser. No. 690,358, filed Apr. 24,1991.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to packaging of semiconductor chips, and inparticular various aspects of the present invention relate to a packagedsemiconductor device, a combination of a semiconductor chip and a leadframe therefor, a method of manufacturing a semiconductor device, and amold for molding a resin package around an assembly of a semiconductorchip and a plurality of lead fingers.

2. Description of the Prior Art

There are a number of known manners of manufacturing a semiconductordevice, in which a semiconductor chip is sealed in a resin package. FIG.4 of the accompanying drawings shows a known "die pad" construction inwhich a chip c is bonded to a die-pad a by a bonding material d, such asa silver paste or a gold-silicon eutectic alloy. The die-pad a isconnected to a peripheral portion of a lead frame by connecting fingersa'. A plurality of lead fingers b project from the peripheral portion ofthe lead frame, and each lead finger b is connected to a respectiveelectrode of the chip c by a respective bonding wire e. The chip c,die-pad a, bonding wires e and inner ends of the fingers a', b are thenplaced in a molding die and sealed in a resin package.

Another known "chip-on-lead" type of construction is shown in FIG. 5. Inthis case, an insulator f, such as a polyimide sheet, is placed on theinner ends of lead fingers b, a semiconductor chip c is placed on theinsulator f and the electrodes of the semiconductor chip c are connectedto respective inner ends of the lead fingers b by respective bondingwires e. Again, the assembly is then sealed in a resin package.

A further known "lead-on-chip" type of construction is shown in FIG. 6.In this case, a surface of a semiconductor chip c, excluding theelectrodes thereon, is covered with an insulator f, lead fingers b areplaced on the insulator f, and the lead fingers b are connected torespective electrodes by respective bonding wires e. Once again, theassembly is then sealed in a resin package.

Lastly, FIG. 7 shows a known "directly connected" form of construction,in which electrode pads g of a semiconductor chip c project upwardlyfrom the upper surface of the chip c, and the inner ends of lead fingersb are directly connected to the electrode pads g. The assembly is thensealed in a resin package.

It is desirable that the height of the semiconductor device is as smallas possible. However, in the die pad construction described above, thethickness of the die pad a and bonding material d add to the height ofthe package. In the chip-on-lead and lead-on-chip forms of constructiondescribed above, the thickness of the insulators f and the lead fingersb add to the height of the package. In the directly connected form ofconstruction described above, the thickness of the lead fingers b andthe height of the electrode pads g add to the overall height of thesemiconductor package. Also, the die pad construction suffers from theproblem that thermal stress is induced in the device due to differencesin the coefficients of thermal expansion of the die pad a, thesemiconductor chip c and the resin of the package, which can cause abreakdown in bonding between the chip c and the die pad a, between thedie pad a and the resin package, or between the chip c and the resinpackage.

OBJECT AND SUMMARY OF THE INVENTION

One object of the present invention is to enable a semiconductor deviceto be produced which has a decreased height.

Another object of the present invention is to alleviate thermal stressesin the semiconductor package.

A further object of the present invention is to enable the semiconductordevice to be produced reliably, such that there is a small risk of thebonding wires being broken or short circuited while the resin package isbeing formed around the assembly of the chip, bonding wires and leadfingers.

In accordance with one aspect of the present invention, there isprovided a semiconductor device, in which the inner ends of the leadfingers lie between the planes of the upper and lower surfaces of thesemiconductor chip, and the resin package directly contacts both theupper surface and the lower surface of the chip. Thus, a reduced heightpackage is provided, and no thermal stress is induced due to thepresence of a die pad.

The lead fingers may be provided by portions of a lead frame, andpreferably additional finger portions are provided which do not normallycontact the chip, but which restrict lateral movement of the chip withrespect to the lead frame during molding of the resin package around theassembly.

In accordance with another aspect of the present invention, there isprovided a mold for molding a resin package around an assemblycomprising a semiconductor chip having a plurality of electrodes, aplurality of lead fingers projecting away from said chip, and aplurality of bonding wires each connecting a respective one of saidelectrodes to a respective one of said lead fingers. The mold comprisesfirst and second complementary mold parts. At least one projectionprojects from at least one of the mold parts interiorly of the moldcavity provided by the mold parts for restricting movement of the chipin the mold cavity when resin is injected into the mold cavity.

Other objects, features and advantages of the present invention willbecome apparent upon consideration of the following detailed descriptionof a preferred embodiment thereof, especially when considered with theaccompanying drawings in which like reference numerals are employed todesignate the same or similar components in the different figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial perspective view of a lead frame to which areconnected a pair of semiconductor chips;

FIG. 2 is a sectional view of a molding die loaded with a lead frame anda semiconductor chip;

FIG. 3 is a sectional view of a resin package as formed by the moldingdie of FIG. 2;

FIG. 4 is a sectional view of a known die pad form of assembly of a leadframe and semiconductor chip;

FIG. 5 is a perspective view of a known chip-on-lead form of assembly ofsemiconductor chip and lead frame;

FIG. 6 is a perspective view of a known lead-on-chip form of assembly ofa semiconductor chip and lead frame; and

FIG. 7 is a sectional view of a known direct connection form of assemblyof a semiconductor chip and lead frame.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIGS. 1 to 3, a lead frame 1 for manufacturing a pluralityof semiconductor devices has apertures 2 for receiving semiconductorchips 7 in a longitudinal arrangement at regular intervals. Theapertures 2 are provided instead of the die pads in the known die padform of construction. Each aperture 2 is of a size such that therespective chip 7 could be passed through the aperture.

The lead frame 1 has peripheral frame members 5 surrounding eachaperture 2, tie bars 4 connecting portions of the lead frame for eachchip, lead fingers 3 projecting towards each aperture 2 and horizontalmovement restricting fingers 6 projecting inwardly from the sideportions of the frame members 5 towards the apertures 2.

Each semiconductor chip 7 is placed in the respective aperture 2. Thesize of the aperture 2 (defined by inner ends of the lead fingers 3 andmovement restricting fingers 6) is such that the lead fingers 3 and themovement restricting fingers 6 do not contact the chip 7.

Each chip 7 has a plurality of electrodes 9, and each electrode isconnected to the inner end of a respective one of the lead fingers 3 bya respective bonding wire 8. Thus, each semiconductor chip 7 isconnected to the lead frame 1 solely by the bonding wires 8.

Then, the lead frame 1, with the chips 7 connected thereto, is placed ina molding die, as shown in FIG. 2. The molding die comprises a lower diepart 10 and a complementary upper die part 11, and the lead fingers andmovement restricting fingers pass through channels 14 between the dieparts 10,11. Both die parts 10,11 are provided with vertical movementrestricting pins 12, which project towards the chip 7, but which areslightly separated from the upper and lower surfaces of the chip 7.After the chip 7 has been placed in the molding die, supported solely bythe lead frame 1 and the bonding wires 8, resin is injected into themold cavity of the molding die to seal the semiconductor chip, thebonding wires 8, and the inner ends of the lead fingers 3 within a resinpackage 13 as shown in FIG. 3.

Although the resin has a sufficiently low viscosity in the initial stageof injection of resin into the mold cavity, the resin tends to urge thechip 7 vertically either towards the lower die part 10 or the upper diepart 11, due to slight differences in resistance against the flow of theresin between the upper and lower surfaces of the semiconductor chip 7.However, vertical movement of the chip 7 is restricted by the verticalmovement restricting projections 12, so that the chip 7 cannotsignificantly move towards the lower die part 10 or upper die part 11.As injection progresses, the resin becomes distributed uniformly withinthe mold cavity, and the resin tends to fill the gaps between the tipsof the vertical movement restricting projections 12 and the upper andlower surfaces of the chip 7. Once injection of the resin has beencompleted, the chip 7 tends to return to its original position withinthe molding die, and therefore partial exposure of the chip 7 at thelocations of the movement restricting projections 12 is unlikely tooccur. The viscosity of the resin being injected may also tend to urgethe chip sideways in the mold cavity. However, sideways movement of thechip is restricted not only by the bonding wires 8, but also by thehorizontal movement restricting fingers 6. Even if the tip of one ormore of the horizontal movement restricting fingers 6 possibly remainsin contact with a side surface of the chip 7 after the resin hashardened, no problem arises because the portions of the horizontalmovement restricting projections which project outside the resin package13 are subsequently cut off.

After the resin has hardened, the lower and upper die parts 10,11 areseparated, and the lead frame with the packages molded thereon areremoved. Then, the horizontal movement restricting portions 6 are cutoff flush with the side of each package 13, and the lead fingers 3 aresevered each at a location spaced from the resin package so as to formindividual connecting leads for the chips.

Having described a preferred embodiment of the invention with referenceto the accompanying drawings, it is to be understood that the inventionis not limited to the precise embodiment and that various changes andmodification thereof may be effected by one skilled in the art withoutdeparting from the spirit or scope of the invention as defined in theappended claims.

What is claimed is:
 1. A method of manufacturing a semiconductor device,comprising the steps of:providing a semiconductor chip, saidsemiconductor chip having an upper surface and a lower surface andhaving a plurality of electrodes; providing a lead frame, said leadframe comprising a peripheral portion surrounding a region for receivingsaid chip and a plurality of lead finger portions projecting from saidperipheral portion towards said region and terminating outside saidregion; placing said chip in said region; connecting each of saidelectrodes to a respective one of said lead finger portions with arespective bonding wire; sealing said chip and bonding wires in a resinpackage such that said lead finger portions project out of said packageand such that the resin package directly contacts both said uppersurface and said lower surface of said chip; and severing each of saidlead finger portions from said peripheral portion of said frame.
 2. Amethod as claimed in claim 1, wherein said sealing step comprises thesteps of:providing a mold having a wall defining a mold cavity and atleast one projection projecting from said wall; placing said chip andbonding wires in the mold cavity such that said projection does notcontact the chip; and injecting resin into the mold cavity; whereby saidprojection restricts movement of said chip in said mold cavity duringsaid injection step.
 3. A method as claimed in claim 1, wherein saidlead frame has a plurality of movement restricting finger portionsprojecting from said peripheral portion towards said region, wherein insaid connecting step said lead finger portions are connected to saidelectrodes such that said movement restricting finger portions do notcontact said chip, and wherein during said sealing step said movementrestricting finger portions restrict movement of said chip in saidregion.
 4. A method of manufacturing a semiconductor device, comprisingthe steps of:providing a semiconductor chip having an upper surface anda lower surface, said semiconductor chip having a plurality ofelectrodes; providing a lead frame, said lead frame comprising aperipheral portion surrounding a region for receiving said chip and aplurality of lead finger portions projecting from said peripheralportion towards said region and terminating outside said region, saidlead finger portions arranged between planes defined by said upper andlower surfaces; placing said chip in said region; connecting each ofsaid electrodes to a respective one of said lead finger portions via arespective bonding wire such that said chip is mechanically connected tosaid peripheral portion solely by said bonding wires and said leadfinger portions; sealing said chip and said bonding wires in a resinpackage such that said lead finger portions project out of said package;and severing each of said lead finger portions from said peripheralportion of said frame.
 5. A method as claimed in claim 4, wherein insaid sealing step the resin package is caused to contact directly bothsaid upper surface and said lower surface of said chip.
 6. A method asclaimed in claim 4, wherein said sealing step comprises the stepsof:providing a mold having a wall defining a mold cavity and at leastone projection projecting from said wall; placing said chip and bondingwires in the mold cavity such that said projection does not contact thechip; and injecting resin into the mold cavity; wherein said projectionrestricts movement of said chip in said mold cavity during saidinjection step.
 7. A method as claimed in claim 4, wherein said leadframe has a plurality of movement restricting finger portions projectingfrom said peripheral portion towards said region, wherein in saidconnecting step said lead finger portions are connected to saidelectrodes such that said movement restricting finger portions do notcontact said chip, and wherein during said sealing step said movementrestricting finger portions restrict movement of said chip in saidregion.